1. Field of the Invention
The present invention relates to a vehicle crash detection apparatus for an Inflatable occupant restraint system.
2. Description of the Related Art
A conventional crash detection apparatus for an inflatable occupant restraint system, or "airbags", makes use of an accelerometer and an offset integrator. The accelerometer generates upon crash impact a signal representative of the vehicle acceleration/deceleration, while the offset integrator subtracts the maximum acceleration value that is encountered during normal drive from the output of the accelerometer and integrates the subtracted acceleration signal over a preset time interval. The integrated signal is then compared with a threshold value and when the threshold is exceeded the restraint system Is operated. Since the airbag must be fully deployed before the occupant is tilted 12.5 centimeters forwards when the vehicle crashes at a medium speed, and the airbag deployment time is approximately 30 milliseconds, there is a small amount of time left for the crash detection apparatus to make a crash/non-crash discrimination.
While the prior art crash detection apparatus is useful for crash events where a sharp vehicle speed variation occurs upon impact, it fails to make a correct discrimination between rough roads and pole crashes where the initial impact on the vehicle is rather small.